There have been various attempts towards the development of high-sensitivity electron beam resists and improvements thereof for microelectronics applications. Considerable work has been directed to the synthesis of electron beam resist by wet chemical methods. Resist based lithography processes are very frequently involved in high resolution lithography techniques, and poly (methyl methacrylate) (PMMA) is one of the polymers most frequently used as a resist for electron beam lithography applications. This type of lithographic process suffers from many limitations, which can extremely constrain the fabrication of sub 100 nm devices. These limitations include resolution limits imposed by the nonuniformity of spin-coated resists, specially when the size of the workpiece is large or has a surface morphology resulting from previous fabrication steps. Resists must have a uniform thickness over the region used for patterning by electron beam lithography. Particularly, radial thickness variation is often associated with the application of resist by spinning.
Among other resists developed to increase sensitivity to electron beam and resolution, chemically amplified resists are one of the predominant types. A major disadvantage of chemically amplified resists is that they are very sensitive to the process conditions (D. Seeger, R. Viswanathan, C. Blair and J. Gelome, “Single Layer Chemically Amplified Resist Processes for Device Fabrication by X-ray Lithography”, J. Vac. Sci. Technol. (1992), B10, pp. 2620-2627). Environmental factors such as airborne amines, time in vacuum system, and time to hydrate as well as extremely tight bake cycle tolerance can strongly affect the resist performance. Furthermore, controllable resist thickness and uniformity for multi-level processing in 3-D (three-dimensional) structure is extremely difficult to achieve using conventional wet resists.
Due to the various disadvantages caused by wet processing methods, dry resist processing has attracted considerable attention in recent years. Dry resist is a desirable alternative to wet processing resist, because it can be processed at ambient temperature; pinhole free film, good adhesion, uniform and ultrathin film deposition are other advantages. Many studies have focused on using plasma deposition to apply electron beam resist on a substrate (see for example: Morita S., Tamano J., Hattori S., et al. “Plasma Polymerized Methyl Methacrylate as an Electron-Beam Resist”, J. Appl. Phys. 51 (7): July 1980, pp. 3938-3941; F. O. Fong, H. C. Kuo, J. C. Wolfe and J. N. Randall, “Plasma Polymerized Styrene; A Negative Resist” J. Vac. Sci. Technol., B 6(1), Dec. 31, 1988, pp. 357-378; Shinzo Morita, Tsuyoshi Naganawa, Jong-Teak Kim, D. C. Lee, and Georgy K. Vinogradov, “Functional Plasma Polymerized Thin Films Prepared by a New Type of Reactor” Proceeding of the 3rd International Conference on Properties and Applications of Dielectric Materials, July 1991, Tokyo, Japan; and S. Gosavi, S. A. Gangal, B. A. Kuruvilla, et al. “Plasma-Polymerized Chlorinated α-Methylstyrene (PP-C-α-MS)—A Performance Negative Electron Resist” Jpn. J. Appl. Phys. 134 (2A), February 1995, pp. 630-635). Other studies used sublimation or thermal evaporation to apply electron beam resists on a substrate (see for example: V. Foglietti, E. Cianci, G. Giannini, “Progress Toward the Fabrication of Scanning Near Field Optical Probe: Pattern Definition by Electron Beam Lightography” Microelectronic Engineering 57-58, September 2001, pp. 807-811). Styrene and its derivatives have shown promising results as electron beam resist (S. Imamura, T. Tamamura, K. Harada and S. Sugawara: J. Appl. Polm. Sci. 27 (1982) 937). Many studies showed improvements in the resolution of the styrene, but the sensitivity is still poor (see for example: F. O. Fong, H. C. Kuo, J. C. Wolfe and J. N. Randall, “Plasma-Polymerized Styrene; A Negative Resist” J. Vac. Sci. Technol., B 6(1), Dec. 31, 1988, pp. 375-378; Shinzo Morita, Tsuyoshi Naganawa, Jong-Teak Kim, D. C. Lee, and Georgy K. Vinogradov, “Functional Plasma Polymerized Thin Films Prepared by a New Type of Reactor”, Proceeding of the 3rd International Conference on Properties and Applications of Dielectric Materials, July 1991, Tokyo, Japan). A high performance negative electron resist using plasma-polymerized chlorinated α-Methylstyrene (PP-C-α-MS) has been reported (S. Gosavi, S. A. Gangal, B. A. Kuruvilla, et al. Jpn. J. Appl. Phys. 134 (2A) February 1995, pp. 630-635). In this study, even the sensitivity is high but the resolution is very poor, and the process requires wet developing of the resist that resulted in undercut.
Plasma polymerized fluoropolymers have been used for various applications other than electron beam resist. As an example, a fluoropolymer thin film deposited by plasma-enhanced chemical vapor deposition (PCVD) has been used as interlayer insulation (U.S. Pat. No. 4,591,547 granted to Brownell in May 1986). Another study used a combination of CF4 and CH4 to deposit a fluorocarbon film for coating (see A. Vanhulsel, E. Dekempeneer, and J. Smeets, “Plasma Polymerization of Fluorine Alloyed Amorphous Carbon Coatings”, J. Vac. Sci. Technol. A 17 (4), July/August 1999, pp. 2378-2383).
Different gases have been used to produce plasma polymerized fluoropolymer thin films. One instance is an article entitled “Mechanisms of Etching and Polymerization in Radiofrequency Discharges of CF4—H2, CF4—C2F4, C2F6—H2, C3F8—H2”, reported by R. d'Agostino, F. Cramarossa, V. Colaprico, and R. d'Ettole through the American Institute of Physics in J. Appl. Phys. 54(3), pp 1284-1288, March 1983. This paper reports some results obtained during the deposition of fluorocarbon films over Si substrates uncoupled from ground in RF plasmas fed with CF4—H2, C2F6—H2, C3F8—H2 and CF4—C2F4 mixtures. Yet another instance is an article entitled “Electrical and Structural Studies of Plasma-Polymerized Fluorocarbon Films” reported by N. Amyot, J. E. Klemberg-Sapieha, and M. R. Wertheimer in IEEE Transactions on Electrical Insulation, Vol. 27 No. 6, pp 1101-1107, December 1992. In this study, plasma-polymerized fluorocarbon films up to 8 μm in thickness have been prepared by high frequency glow discharge deposition to investigate the charge storage properties of the material. Yet another instance is an article entitled “The Properties of Plasma-Polymerized Fluorocarbon Film in Relation to CH4/C4F8 Ratio and Substrate Temperature” reported by Y. Matsumoto, M. Ishida, Sensors and Actuators A: Physical, Vol. 83 (1-3) May 22, 2000, pp. 179-185. In this study, plasma polymerized fluorocarbon films have been deposited with a deposition rate as low as few nanometers per minute.